The present invention relates to gas turbine power plants and, more particularly, to such plants which are arranged for dead load pickup.
In various areas of a power system, it may be desirable to provide a local generating plant to produce power for the area in the event the area becomes isolated from the rest of the system by a transmission line outage. In this way, the health and safety and convenience needs of the people served by the power system area can be reasonably met during the outage. Similarly, many large industrial plants such as metal processing plants have a need for local replacement generation in the event of a loss of the external power supply to such plants. Even steam power generating plants have a need for replacement power to operate auxiliary equipment during black plant starts after a shutdown of the steam turbine-generator equipment.
When an outage occurs, a plant which is to be brought on line to replace the lost generation often must be controlled to accept a dead load, i.e. in a power system a load already connected to the lines made dead by the transmission line outage. Gas turbine power plants are well-suited to providing replacement power because they can be started rapidly and they can provide relatively large amounts of power for replacement purposes for a part of the power system.
Residential dead load pickup by single gas turbine power plants has been performed previously in 1972 at the VEPCO Kitty Hawk plant in North Carolina. In such plant starts, the gas turbine control is triggered to accelerate the turbine to a speed above synchronous speed and the generator breaker is closed to connect the dead area load to the generator. The load placed on the turbine causes the turbine speed to droop to near the synchronous speed value, and the turbine speed control enters an isochronous mode to meet the load demand and hold the bus to the desired operating frequency, i.e. 60 Hertz.
If multiple gas turbines are to be started for dead load pickup in the same area, it is desirable that they be operated in a coordinated way during the startup and load modes of operation. Further, simultaneous synchronization of two or more generators must be avoided since it can cause damage if the generator breakers close when the associated generators are not matched in voltage magnitude, frequency or phase.
No known prior art publications and no known prior art power plants have included structure directed to this purpose. The Kitty Hawk plant has included a design capability for coordinated multi-unit dead load pickup by two gas turbine power plants and some descriptive information has been provided to the customer. However, the installed coordinated dead load pickup system has had an experimental status, i.e. there has been only a few days in each year during which the dead load pickup system can be scheduled for testing and as of the Fall of 1975 parts of the system such as acceleration to 108% speed, certain logic controls, the isochronous control and load rate limiting action have been verified in single unit starts and dead load pickup but the coordinated system for multiple unit starts and dead load pickup had not been properly operated nor accepted by the customer. On July 17, 1973, the two units were operated in the load mode together on an experimental basis, but the first unit was synchronized and moved to a load of 5 MW before the second unit was synchronized to the first unit. Thereafter, the two units shared an 8 MW load for about 15 minutes and because of load variance on the second unit and inability to synchronize to the tie line, the two units were shut down and the experiment was ended. Description of the prior art herein is presented in good faith and no representation is made that it is the best prior art not that interpretations placed on it are unrebuttable.